Flap-gate valves are used in industrial settings to transport dry particulate matter. Essentially, they comprise a mechanical arm, pivotally mounted at one end and having a flap (also sometimes referred to herein as a “flapper”) affixed to the other end. The arm rotates to move the flap into and out of engagement with the bottom opening of a structure known as a seat. When the flap is not engaged with the seat, any particulates in the seat are free to flow through the bottom opening. When the flap engages with the bottom opening of the seat, a seal is formed, preventing the contents of the seat from passing through the bottom opening. In other words, the seat is essentially a temporary receptacle with an opening at the top for receiving particulate matter, and a bottom which is open when the flap is not engaged and closed when the flap is engaged. In many cases, the width of the seat tapers down from the top to the bottom, in a funnel-like manner.
When connected in serial and operated in sequential fashion (a “double flap-gate valve”), flap-gate valves are capable of maintaining a pressure differential between two environments, while transporting matter across the environments. Given this application, a key aspect of such valves is to maintain an air-tight seal between the two environments. For example, flap-gate valves are used in the removal of dust accumulations in industrial plants, as key components in the discharge lines of vacuum dust collection systems. Over time, and particularly with abrasive particulates, the surfaces of the seat and/or flap are worn away and the flap is no longer able to form an air-tight seal with the seat. Flap-gate valves were originally used for dust collection and this improvement added to the ability of the valve to operate in new applications, such as pneumatic conveying.
The following background technology shows what we believe would be known to a worker skilled in the art of the present invention, and accordingly need not be detailed further herein:
U.S. Pat. No. 3,257,045: DUST TRAP AND VALVE THEREFOR, issued Jun. 21, 1966, discloses a dust trap and valve, and more specifically a dust valve which is said to allow the inspection, cleaning, and/or replacement of its wearing parts without disconnecting or removing the entire trap unit from its working position or completely disassembling the dust trap unit.
U.S. Pat. No. 4,304,254: DUST TRAP VALVE WITH REMOVEABLE DOUBLE LIFE DOOR AND VALVE SEAT MEMBER, issued Dec. 8, 1981. This patent discloses a dust valve for the discharge line of a dust collection system, including a removable closet with two wear surfaces and a coacting removable valve door with two wear surfaces mounted within the valve body. Once the coacting wear surfaces on the closet and the door are sufficiently worn that they need replacement, each element can be disconnected from its supporting structure, inverted, and then reconnected to the valve body so as to expose a new wear surface. The useful lives of these elements are thus doubled over conventional single wear surface closets and doors.
U.S. Pat. No. 4,307,747: DUST TRAP WITH REMOVABLE VALVE SEAT, issued Dec. 29, 1981, discloses a dust trap for bag houses and the like which is provided with an internal removable valve seat to facilitate replacement of the valve seat or regrinding of the valve surface. The valve seat and dust trap have complementary supporting parts to support the valve seat while it is being removed from or replaced in the dust trap.
U.S. Pat. No. 4,945,949: REDUCE HEIGHT DUST VALVE, issued Aug. 7, 1990. This patent discloses a dust trap comprising a pair of coaxially mounted dust valves. Each valve has a valve seat and flapper plate and actuator shaft which coacts with the flapper plate to cause it to initially slide and then pivot as the valve opens.
U.S. Pat. No. 5,241,989: REDUCED HEIGHT DOUBLE-FLAP DUST VALVE, issued Sep. 7, 1993, discloses a reduced-height dust valve used in a trap which utilizes a pair of said valves to remove dust from, for example, a vacuum line. The valve includes a body having a longitudinal flow path, a valve seat detachably mounted in the upper portion of the body and opposed flapper plates which seat against each other to close the valve or are rotated downwardly by actuator shafts to open the valve. The flapper plates define adjacent edges which seat against each other by a sliding action permitted by movement of one of the two actuator arms.